This invention relates generally to new and improved apparatus and process for providing the internal portion of tubing with at least one internal spiral groove, and more particularly relates to new and improved apparatus and process for providing the internal portion of tubing with at least two internal spiral grooves to provide said tubing internal portion with at least one internal spiral fin, preferably a plurality of internal spiral fins.
Tubing provided with one or more internal spiral fins is known to the art and, as is further known, such tubing typically is referred to in the art as enhanced tubing, and such enhanced tubing has many different known applications. An example of such enhanced tubing is illustrated diagrammatically in FIGS. 1 and 2 and is identified generally by numerical designation 10. Tubing 10 is provided with a plurality of internal spiral fins illustrated diagrammatically and identified by general numerical designation 12; it will be understood that the size of the fins 12 with respect to the tubing 10 has been exaggerated in FIG. 2 but such is done for the sake of clarity and ease of illustration. A well known prior art application for enhanced tubing 10 is for utilization as heat exchanger tubing with the internal spiral fins 12 providing enhanced thermal exchange between the tubing 10 and a fluid flowing therethrough such as air conditioning fluid.
Prior art apparatus and process for providing tubing 10 with internal spiral grooves 12 are illustrated diagrammatically in FIG. 3. Draw blocks or blocks 14 engage the tubing 10 and apply pulling or draw force, indicated by arrows 16, to pull or draw the tubing between a draw die 20 and a floating plug or mandrel 22. As is known to those skilled in the art, such drawing imparts rotation to the floating plug or mandrel 22 and the forward portion of the floating plug or mandrel 22 is of reduced diameter and provided with a plurality of external spiral lands or ridges 24 which engage the internal portion of the tubing 10 and form a plurality of spiral ridges therein which provide the tubing internal portion with a plurality of internal spiral fins, such as fins 12 of FIGS. 1 and 2. During such prior art drawing, as is known, considerable friction is developed between the internal portion of the tubing 10 and the spiral lands or ridges 24, such friction being identified by arrow 26, and in addition considerable friction or frictional resistance to rotation is developed between the external surface of the floating plug or mandrel 22 and the internal surface 28 of the tubing 10, such friction is indicated by arrow 29. These frictions, or frictional forces, as is known to those skilled in the art, typically do not permit the desired rotation between the floating plug or mandrel 22 and the tubing 10 which tubing does not rotate and instead moves only linearly in the direction of the drawing forces 16. This resistance to plug or mandrel rotation inhibits undesirably the drawing rate which may be achieved and further inhibits undesirably the depth of the spiral grooves, and hence the height of the internal spiral fins 12, which may be formed by this prior art apparatus and process.
Other prior art apparatus and process for providing tubing with internal spiral fins is that of swaging and shear spinning over a grooved mandrel; typically undesirably poor fin definition is achieved by this approach, and as is also known to those skilled in the art, this approach is relatively slow compared even to the above-noted prior art drawing approach illustrated diagrammatically in FIG. 3.
Accordingly, there exists a need in the art for new and mproved apparatus and process for providing the internal portion of tubing with at least one internal spiral groove, or at least one internal spiral fin, and preferably a plurality of internal spiral fins.